Typically, an external cavity tunable laser source is used to characterize passive optical components. Generally, the tunable laser is swept across the wavelength of interest and the resulting signal change in power can be converted to insertion loss versus wavelength.
An external cavity laser can be made such that most of its power is in a single mode, with very small sideband signals. As such, the sideband signals are so small as to have an insignificant effect on the measurement of the passive optical component. Tunable lasers based on Vernier-tuned Bragg Reflector (VTDBR) monolithic tunable lasers are being developed. Such lasers may be referred to herein as Semiconductor Monolithic Tunable Laser Source (SMTLS). There are some advantages to these, including speed of the sweep and cost reduction over conventional lasers. However, the sideband signals are larger with SMTLS lasers, which can degrade the quality of the measurement. This degradation is due to the unwanted effects of the sideband signals.